Racemic [fluoro(hydroxyphenylphosphinyl)methyl]phosphonic acid (1) and its individual enantiomers [(+), 98% ee; (-), 67% ee] were previously shown to inhibit Na(+)-gradient-dependent Na(+)-phosphate cotransport across renal brush border membrane, without measurable stereospecificity. Resolution of 1 was effected by fractional recrystallization of its (-)-quinine salts. The more levorotatory, diquinine product 2, corresponding to (+)-1, has now been analyzed by X-ray crystallography and found to be composed of the S enantiomer of 1. This result confirms the absence of stereochemical preference in inhibition of the cotransporter by the enantiomers of 1 and provides the first absolute configuration assignment of an asymmetrical alpha-halomethylene pyrophosphate analogue.